The extracellular matrices of calcified tissues contain macromolecules which spatially and temporally regulate mineralization and osteogenesis. The overall objective of this project is to elucidate the regulatory properties of these macromolecules in terms of their structure and physico-chemical properties. Our goals for this year were: to examine the conformational dependency of the complementarity between positively and negatively charged groups in purified collagen; to characterize the interaction between phosphate ions and purified collagen; and to characterize the calcium binding properties of the phosphoproteins of dentine. Findings of the studies conducted during the year indicated: the complementarity between charged side chains in collagen was strongly dependent on the conformation of the native structure; the net association of phosphate ions with purified collagen could be accounted for in terms of coulombic effects between the positively charged collagen fibrils and negatively charged ions; and that the extractable phosphoproteins had different calcium binding properties than the phoproteins associated with dentinal collagen. These studies are now being extended to various collagenous tissues.